Classification of Organisms in Biology

Classifying Organisms in Order

• Biological classification systems organize living organisms into hierarchical groups based on shared characteristics and evolutionary relationships.
• This hierarchy typically includes: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species (remembered by the mnemonic "Dear King Philip Came Over for Good Soup").
• Classification aims to reflect the evolutionary history and genetic relatedness of organisms.
• Modern classification methods often utilize phylogenetic trees or branching diagrams to illustrate evolutionary relationships.

Bacteria and Archaea

• Bacteria and Archaea are two of the three domains of life, distinct from the eukaryotes.
• Bacteria are ubiquitous and diverse, playing crucial roles in nutrient cycling and ecosystems.
• Archaea are extremophiles, thriving in extreme environments like hot springs, salt lakes, and anaerobic conditions.
• Both bacteria and archaea are prokaryotes.

Branching Diagrams

• Branching diagrams, also known as phylogenetic trees, visualize evolutionary relationships.
• These diagrams depict the divergence of species from common ancestors.
• Branching points represent speciation events (the formation of new species).
• The length of the branches can represent time or genetic distance.
• Often, diagrams use shared derived characteristics to arrange organisms. Shared derived characteristics are characteristics that were not present in a common ancestor but are present in organisms further down the branch.
• Branching diagrams help scientists understand the evolutionary history and relationships of different organisms.

What is a Prokaryote?

• Prokaryotes are single-celled organisms lacking a nucleus and other membrane-bound organelles.
• Their DNA is typically circular and located in a region called the nucleoid.
• Prokaryotic cells are generally smaller and simpler than eukaryotic cells.
• They are the most abundant organisms on Earth.

Differences Between Eukaryotic and Prokaryotic Cells

• Cellular Structure:
  • Prokaryotic cells lack membrane-bound organelles like mitochondria, chloroplasts, endoplasmic reticulum, and Golgi apparatus.
  • Eukaryotic cells possess these organelles.
• DNA Organization:
  • Prokaryotic DNA is typically circular and not enclosed within a nucleus.
  • Eukaryotic DNA is linear and enclosed within a nucleus.
• Size:
  • Prokaryotic cells are generally smaller than eukaryotic cells.
• Complexity:
  • Prokaryotic cells are structurally simpler than eukaryotic cells.
• Reproduction:
  • Prokaryotes typically reproduce asexually through binary fission.
  • Eukaryotes typically reproduce sexually or asexually, with varying mechanisms.
• Cell Wall Composition:
  • Prokaryotic cell walls are composed of peptidoglycan (in bacteria) or other materials.
  • Eukaryotic cell walls (where present) have different composition, such as cellulose in plants or chitin in fungi.